Immunoglobulins are comprised of four polypeptide chains, two heavy chains and two light chains, which associate via disulfide bonds to form tetramers. Each chain is further comprised of one variable region and one constant region. The variable regions mediate antigen recognition and binding, while the constant regions, particularly the heavy chain constant regions, mediate a variety of effector functions, e.g., complement binding and Fc receptor binding (see, e.g., U.S. Pat. Nos. 6,086,875; 5,624,821; 5,116,964).
The constant region is further comprised of domains denoted CH (constant heavy) domains (CH1, CH2, etc.). Depending on the isotype, (i.e. IgG, IgM, IgA IgD, IgE) the constant region can be comprised of three or four CH domains. Some isotypes (e.g. IgG) constant regions also contain a hinge region Janeway et al. 2001, Immunobiology, Garland Publishing, N.Y., N.Y.
The creation of chimeric proteins comprised of immunoglobulin constant regions linked to a protein of interest, or fragment thereof, has been described (see, e.g., U.S. Pat. Nos. 5,480,981 and 5,808,029; Gascoigne et al. 1987, Proc. Natl. Acad. Sci. USA 84:2936; Capon et al. 1989, Nature 337:525; Traunecker et al. 1989, Nature 339:68; Zettmeissl et al. 1990, DNA Cell Biol. USA 9:347; Byrn et al. 1990, Nature 344:667; Watson et al. 1990, J. Cell Biol. 110:2221; Watson et al. 1991, Nature 349:164; Aruffo et al. 1990, Cell 61:1303; Linsley et al. 1991, J. Exp. Med. 173:721; Linsley et al. 1991, J. Exp. Med. 174:561; Stamenkovic et al., 1991, Cell 66:1133; Ashkenazi et al. 1991, Proc. Natl. Acad. Sci. USA 88:10535; Lesslauer et al. 1991, Eur. J. Immunol. 27:2883; Peppel et al. 1991, J. Exp. Med. 174:1483; Bennett et al. 1991, J. Biol. Chem. 266:23060; Kurschner et al. 1992, J. Biol. Chem. 267:9354; Chalupny et al. 1992, Proc. Natl. Acad. Sci. USA 89:10360; Ridgway and Gorman, 1991, J. Cell Biol. 115, Abstract No. 1448; Zheng et al. 1995, J. Immun. 154:5590). These molecules usually possess both the biological activity associated with the linked molecule of interest as well as the effector function, or some other desired characteristic associated with the immunoglobulin constant region (e.g. biological stability, cellular secretion).
The Fc portion of an immunoglobulin constant region, depending on the immunoglobulin isotype can include the CH2, CH3, and CH4 domains, as well as the hinge region. Chimeric proteins comprising an Fc portion of an immunoglobulin bestow several desirable properties on a chimeric protein including increased stability, increased serum half life (see Capon et al. 1989, Nature 337:525) as well as binding to Fc receptors such as the neonatal Fc receptor (FcRn) (U.S. Pat. Nos. 6,086,875, 6,485,726, 6,030,613; WO 03/077834; US2003-0235536A1).
FcRn is active in adult epithelial tissue and expressed in the lumen of the intestines, pulmonary airways, nasal surfaces, vaginal surfaces, colon and rectal surfaces (U.S. Pat. No. 6,485,726). Chimeric proteins comprised of FcRn binding partners (e.g. IgG, Fc fragments) can be effectively shuttled across epithelial barriers by FcRn, thus providing a non-invasive means to systemically administer a desired therapeutic molecule. Additionally, chimeric proteins comprising an FcRn binding partner are endocytosed by cells expressing the FcRn. But instead of being marked for degradation, these chimeric proteins are recycled out into circulation again, thus increasing the in vivo half life of these proteins.
Portions of immunoglobulin constant regions, e.g., FcRn binding partners typically associate, via disulfide bonds and other non-specific interactions, with one another to form dimers and higher order multimers. The instant invention is based in part upon the surprising discovery that transcytosis of chimeric proteins comprised of FcRn binding partners appears to be limited by the molecular weight of the chimeric protein, with higher molecular weight species being transported less efficiently.
Chimeric proteins comprised of biologically active molecules, once administered, typically will interact with a target molecule or cell. The instant invention is further based in part upon the surprising discovery that monomer-dimer hybrids, with one biologically active molecule, but two portions of an immunoglobulin constant region, e.g., two FcRn binding partners, function and can be transported more effectively than homodimers, also referred to herein simply as “dimers” or higher order multimers with two or more copies of the biologically active molecule. This is due in part to the fact that chimeric proteins, comprised of two or more biologically active molecules, which exist as dimers and higher order multimers, can be sterically hindered from interacting with their target molecule or cell, due to the presence of the two or more biologically active molecules in close proximity to one another and that the biologically active molecule can have a high affinity for itself.
Accordingly one aspect of the invention provides chimeric proteins comprised of a biologically active molecule that is transported across the epithelium barrier. An additional aspect of the invention provides chimeric proteins comprised of at least one biologically active molecule that is able to interact with its target molecule or cell with little or no steric hindrance or self aggregation.
The aspects of the invention provide for chimeric proteins comprising a first and second polypeptide chain, the first chain comprising at least a portion of immunoglobulin constant region, wherein the portion of an immunoglobulin constant region has been modified to include a biologically active molecule and the second chain comprising at least a portion of immunoglobulin constant region, wherein the portion of an immunoglobulin constant region has not been so modified to include the biologically active molecule of the first chain.